INFLUENCE OF ALPHA-TOCOPHEROL ON LIPID OXIDATION PATHWAYS

Abstract

In this study, the focus was the qualitative and quantitative analysis of epoxides, hydroxides and aldehydes produced during oxidation of a single triacylglycerol, trilinolein, in the presence and absence of alpha-tocopherol, to better understand the diversity of products produced and the rates of their formation. Although alpha-tocopherol has a well-known antioxidant effect at low concentrations, it may also function as a prooxidant at high concentrations. To address this, alpha-tocopherol was added to trilinolein at two concentrations (0.1% and 2% by mass) and compared to a control sample without added tocopherol. All the samples were heated at 30 degree Celcius with aliquots removed for analysis every 3 days in a 15-day experimental cycle. Results clearly demonstrated the antioxidant capacity of α-tocopherol at 0.1%, with oxidation products present in lower concentrations and increasing more slowly than in the other treatments. Although earlier formation of hydroxides and aldehydes was obvious in samples treated by 2% α-tocopherol, the prooxidant capacity of α-tocopherol could not be statistically proven because of the high variation between replicates. The absence of epoxides and the presence of epoxy-hydroxy lipids suggested that the formation of hydroperoxides, accelerated by high concentrations of tocopherol, dominated over alternative oxidation pathways. Further, only one type of aldehyde was identified and quantified successfully and its concentration was much higher than the other products. Its structure suggested that the decomposition of hydroperoxides led to formation of hydroxides, epoxy-hydroxy lipids and finally aldehydes, in a step-by-step process. Hence, the formation of aldehydes reduced the concentrations of the other products, which might influence conclusions about tocopherol’s prooxidant activity. Further investigation will be carried out by identifying and quantifying hydroperoxides to prove the alteration of the oxidation pathways in this study.